The coolant demand of a combustion engine depends on many factors, such as engine temperature, environment temperature, effective engine power etc. A mechanical coolant pump is directly driven by the internal combustion engine so that the rotational speed of the pump is strictly proportional to the rotation speed of the combustion engine. As a consequence, the mechanical coolant pump does not consider the coolant demand of the combustion engine.
More sophisticated mechanical coolant pumps are therefore made adjustable by different kinds of valve mechanisms. WO 2007/025375 A2 describes an adjustable mechanical coolant pump with pivotable pump stator blades surrounding the pump rotor wheel. The stator blades form an inlet valve so that the coolant flows through the open inlet valve before it is pumped by the pump rotor wheel radially inwardly. However, when the stator blades are in the closed position and the rotor wheel is rotating with high speed, cavitation can occur which causes undesirable effects.
The stator blades are pivotably mounted axially between two mounting rings and are pivoted by a separate control ring surrounding one mounting ring. During the assembly procedure, the control ring can fall off the mounting ring as long as the mounting rings and the control ring are not fixed to the pump housing body. When the control ring falls off, every single stator blade must be re-assembled with the control ring, which is a time consuming procedure.